18 Volts + ! Need ideas please

[Southbound]

Need Help! Not long ago I noticed my check-engine light came on and when looking at my guages I noticed that my volt meter was reading 18+ volts. This will happen at radom times and usually will stay on 18+ volts for a minute and then return to its normal position and obviously the check-engine light will turn off. I took it to the dealer where they replaced the PCM?? which is where the voltage regulator resides. After picking it up and driving it home the problem is still there. I have had the alternator checked at a local alternator shop ... . the alternator checked out ok. Any ideas?



Southbound

 

[Vaughn MacKenzie]

Southbound, doesn't sound like the dealer got to the root of the problem. I would take it back and insist they fix it right (esp. if it's still under warranty). I don't know a lot about alternators but if you had a basic voltmeter you could check the voltage at the batteries. They both should measure around 14. 5 volts at normal charge (check with engine running a few minutes after you fire up so voltage stabilizes). What the voltmeter on your instrument panel reads should be pretty close to what you read at the batteries.



If you check it when your meter reads 18V and you measure 18v at your batteries you need to get it fixed ASAP! Running that high of voltage can kill your batteries in no time and you run the risk of them blowing up on you



Vaughn

 

[BK]

Sorry I don't have a direct answer... but this is how I would start...

Is the Voltage guage really correct? When it happens use a real volt meter at both the battery(ies) and say the cig lighter... to double check.



Start checking all your ground connections.

Chassis to engine.

Question that I'm not sure about. . does the ecm get it's ground from it's mounting screws?. . are those mounting screws tightening well.

Check the plugs/connectors at the alternator. Mounting bolts of the alternator ground it to the block. . are they all tight?

Check you battery terminal connections.

Not only that they arent corrrioded... but that wire can not be removed from the lead connector.



Also I noticed during my 2nd to last oil change, while checking out the truck, that the negative wire from the passanger side battery goes to a lug thats bolted to the lower side of the block... under the oil filter. . Right next to the oil return line from the turbo.

It was filled with oil residue. There's no star washers to cause deep penatrating connections either. So an oily film there can cause a bad ground while the bolt is still tight.

 

[15w40]

One other possibility is the battery temperature sensor. This measures the temperature under the driver’s side battery and sets the charging voltage level. This sensor is called an RTD and raises its resistance as temperature goes down. If it becomes disconnected the PCM will put out the maximum charging voltage, thinking that it is REALLY COLD. Try wiggling the wire to this sensor while someone watches the voltmeter on the dash.

 

[BK]

15w40 ,

Nice one, I honestly didn't know it was there.

Learn something new everyday.

Seems like a good possibility.



The FSM doesnt say if it's a PTC or an NTC. .

If we knew, could tell for sure if when unplugged if the battery voltage would go high or low.

 

[Southbound]

18 volts +

Thanks again for all of your replies. I actually dropped my truck off to the dealer yesterday for them to do some more research on it. I actually just called the service manager and discussed with him some of the suggestion you guys mentioned in your post. 15W-40 great idea on the sensor... . didnt even know there was such a thing??? I will keep you guys posted on the findings. Please keep the suggestions coming!! Thanks again for all of your help. TDR Rocks!!!!!



Regards,



Southbound

 

[BK]

Southbound,

Good luck withe the dealer on this one. My experiance on such problems. . they usually can't find it. I hope for your sake they do without much problem. I hate to see them do more knee jerk repairs via northwest to southeast trouble shooting meathod.

 

[C Schomer]

Make sure the batt terminals are clean and tight and all other connections between the alt and batteries, regulator and grounds. Cables can also go bad - corrosion under the insulation. A bad battery can also drive the charging nuts but in our case, it would have to be two bad batteries. I've had these kind of problems and a new battery fixed them! The 15-40 RTD idea is a good one! RTDs aren't very dependable. The 100 ohm RTDs are especially bad. 1000 ohm RTDs are better material - at least the ones I work with. You can put an ohmmeter on them and heat them up and watch the ohms go up - should be steady rise. Bad ones will flake out, at some point. I can bring an RTD table home if you need to know the exact values. Craig

 

[Southbound]

Update

Just an update: The dealer is still working on my truck ... ... it has been determined that my truck will register 18+ volts when the motor is running over 2000 RPM????? They have checked battery terminals, battery temp. sensor, and have replaced PCM so far. I will keep you guys posted... please keep your fingers crossed.



Southbound

 

[BK]

Very interesting.

I'm going to guess that they will find a bad alternator.

They already replaced the PCM. . that would have been a good 1st guess based on it going nuts at 2000 rpm.

But since that's been replaced...

I know you said a shop tested it, But with the issue of it being rpm based. . I might guess you either have some diodes going real noisy and recovery time falling apart causing the noise. And the noise is driving the PCM crazy...



Still could be a bad ground. . resistance being a bit high.



Thats my WAG with out being able to touch it.



It will be really cool to hear the solutions.

Looking forward to your update.

Good to see they can repeat it for you.



Bob

 

[Southbound]

FIXED!!!!!!!!!!!!!!!!!!!!!!!!!!

GOOD NEWS!! Got my truck back and is running great!! Now for the solution... ... turns out that there was a cable loose which runs from the battery terminal to the PDC (Power Distribution Center) which is located on the driver side fender. Apparently this cable would shake loose thus causing the 18 volts + problem. You know it always the most simple things that cause the most problems. I got to give a thumbs up to Mickenny Dodge of Mickenny TX for sticking it out on their research of the problem. I would have gave up a long time ago!!! Note: to all fellow members ... check this connection because the shop had mentioned that there was a truck that just arrived as I was leaving which had the same problem. Thanks again to all of you that responded... . I was desperate for a solution. Put 300 miles on my truck today... . sure feels good to be back in the ultimate machine CTD!!!!!!!!! Take care and God Bless,



Southbound

 

[BK]

Thanks for posting the results and letting us all know.

Glad to see you had a dealer that did the job for you.